The traveling systems for engineering machines such as wheel loaders include one described in Patent Document 1. The traveling system disclosed therein comprises a diesel engine and a travel device having a Hydro-Static Power Transmission (HST) driven by the engine. The HST includes a hydraulic pump driven by the engine, at least one hydraulic motor of a variable-displacement type that is connected in a closed circuit to the hydraulic pump, and a clutch unit coupled to an output shaft of the hydraulic motor. The HST transmits the motive power of the engine to the axle of wheels hydromechanically.
Also, the commercialized traveling systems for wheel loaders and other engineering machines include a type comprising a torque converter and a transmission and constructed to transmit the motive power of an engine to the axle of wheels hydromechanically.    Patent Document 1: JP, A 11-230333